1. Field of the Invention
The invention relates to an improved process for the preparation of hydroxycitronellol by the addition reaction of water with citronellol.
2. Brief Description of the Prior Art
The U.S. Pat. No. 4,200,766 describes the preparation of hydroxycitronellol by the addition reaction of water with citronellol, in the presence of an alkanol solvent and a cation exchange resin catalyst and is representative of prior art methods.
Prior art methods of hydrating citronellol have not been completely satisfactory. The major problems associated with the prior art processes relate to (1) low conversions (about 60 percent yields) and (2) contamination with by-product ethers. The major by-product of the hydration is citronellyl alkyl ether. This by-product, even in low concentrations, adversely affects the odor of the desired product, hydroxycitronellol and the aldehyde made from it, hydroxycitronellal.
By the method of the present invention, the hydration of citronellol to obtain hydroxycitronellol may be carried out, without the formation of contaminant ethers and in high yield. In a preferred embodiment method of the invention, acetone is employed as the solvent for the citronellol reactant. This preferred method has particular advantages over prior art methods. For example, we have found that acetone is an excellent solvent for water, citronellol, and hydroxycitronellol so it allows one to add additional water (up to about 4 parts to one part citronellol and 2 parts acetone) to the reaction mixture, as the reaction proceeds, without loss of homogeneity. That you can use so much water and so little acetone is surprising and boosts conversion to as much as 72 percent. In addition, one can extract the final product solution with an immiscible, non-polar hydrocarbon such as heptane. Unreacted citronellol is concentrated in the hydrocarbon layer and product hydroxycitronellol is concentrated in the acetone-water layer. In this way a product containing 90% hydroxycitronellol is easily made. Citronellol in the heptane layer is easily recovered and recycled.